1. Field of the Invention
The present invention relates to a hinge fitting for foldable ladders.
2. Description of the Prior Art
In one known hinge fitting (West German Utility Model No. 78 11 073), as a result of the locking device, the two lock bolts need not, for automatic locking in a different swing position be brought before the start of the swinging movement, into the boreholes associated with the new position of swing, but need only be brought into the unlocked position. This known hinge fitting is, however, expensive and, in particular is trouble-prone. For example, the guidance of the guide pin, developed as a relatively thin pin, within the hinge pin is poor since the diameter of the central opening in the end of the hinge pin through which the guide pin is brought out is adapted to the larger diameter of a conical section which is required in order to spread apart a hairpin-shaped spring forming the spring locking element to such an extent that it can engage in an annular groove in the guide pin. The poor guidance of the guide pin can lead to the canting of the locking bolts. The problem is, however, also due to the fact that the hollow hinge pin is made of plastic because of its complicated shape. This complicated shape is in part due to the mounting of the hairpin-shaped spring in two diametric slots in the hinge pin directly adjacent the end thereof, but in particular also to the projections provided within the hinge pin, extending in its longitudinal direction, which are required together with projections on a disk provided on the end of the guide pin opposite the handle in order to bring the hairpin-shaped spring back out of engagement with the annular groove of the guide pin before, upon a swinging motion of the parts of the fitting relative to each other, the next position is reached in which the fitting parts can be locked. As soon as the unavoidable wear of the plastic projections has reached a certain degree the locking device will no longer open. The fact that the hinge pin consists of plastic is, however, also disadvantageous insofar as, due to this, the hinge pin is not guaranteed against breakage and its operability can be impaired by influences of temperature. Another disadvantage is that due to the force-held engagement of the hairpin-shaped spring into the annular groove, the force of the return spring must be correlated to the holding force of the locking device which, together with the plate required at one end of the guide pin, leads to a relatively large axial length of the hinge pin. Finally it should also be mentioned that external disturbing influences, for instance grease which has penetrated into the mounting pin, can cause the locking device no longer to operate dependably.